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Old 3rd April 2006, 04:32 PM   #1
elaar is offline elaar  United Kingdom
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Join Date: Oct 2005
Default outboard power supply

Hi all,

I'm building a gainclone (my first attempt) and am using 2 toroidal transformers (1 for each channel), and am putting the power supply module in a seperate case, so that the main amp will fit in a nice small aluminium enclosure I already have.

My question is how exactly should I seperate this? Some people say that to keep EMI to a minimum I should place all AC components seperate (toroidals, main filter capacitors, rectifiers...) from the main amplifier components.
However, this would mean a long(ish) run of cable form the psu to the amp carrying DC which i believe is more susceptible to interference etc.. ALSO can't oscillation become a problem when chip-amps are quite a distance from the main power caps? or is this just with very high bandwidth buffer opamps?
With my limited knowledge I would have thought that putting the toroidals on their own would be the best bet with a small amount of AC components in the amp case so that the mains power caps are close to the chip-amp, but then what do i know Smile

Many thanks in advance
Andy
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Old 3rd April 2006, 04:40 PM   #2
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if you carefully dress the leads in a power amplifier you won't pickup any a.c. from the mains -- the best way to check for a.c. is with a distortion analyzer -- looking for the distortion at the harmonics of the mains frequency.

if you must use separate cabinets use a FEMALE receptacle on the power supply, a MALE plug into the power supply -- put bypass capacitors on the power receptacle and at the point at which it enters the amplifier cabinet. when I had separated a solid state amplifier from its power supply I used a 3-conductor industrial extension cord cut to a convenient length.

the problem with long leads is that you waste energy as heat --
R * I^2 just like the electrical utilities -- better to put the amps into the music.
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Old 3rd April 2006, 04:48 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
put the transformers and rectifiers and first stage smoothing in the remote PSU box.

Put second stage (high quality) caps beside/on top of the chipamp. These are effectively the decoupling caps that are normally on board.

The remote + decoupling form an RCRC PSU which can have less hum than a simpler RC supply.

The smoothing beside the rectifiers have a very high ripple so ensure you provide sufficient ripple capacity. Lots of small parallel caps can achieve this cheaply.

The local decoupling need low esr to enable the amp to source peak current and should preferably have more total capacitance than the first stage smoothing.

Hope this gets you started.
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